Question of the Week Number 2: February 7, 2019
“Is it time yet to apply pre-emergent granules for weeds? It’s been so warm, and I’m seeing weeds all over my yard.”
It seems like all I’m hearing about right now is winter weeds and pre-emergents. Please let me cite a few facts that may put us back on course.
• There are two categories of weeds based on when they show up in our lawns. They are either “cool-season” weeds or “warm-season” weeds. It’s cool outside now, so you’re seeing “cool-season” weeds.
• There are two categories of weeds based on how long they live. “Annual” weeds germinate, grow and complete their life cycles in one of their growing seasons. “Perennial” weeds come back from roots – that is, the same plant survives from one growing season to the next. Pre-emergents are only effective on annual weeds.
• The weeds you’re seeing out in your lawn right now are almost all annual weeds.
• Pre-emergent means “before” something emerges. In this case, it means before it germinates, or sprouts. That’s important when you’re dealing with annual weeds.
• Timing. Here is the critical part. You must apply pre-emergent granules just before annual weed seeds start to germinate.
For the weeds you can see now… Those are cool-season weeds that germinate in fall, so that application must be made the last week of August through the first week of September. Dimension, Halts or Balan for grassy weeds. Gallery for broadleafed weeds.
For the weeds that will germinate as it gets warmer… In most parts of Texas we’re worried mainly about crabgrass and grassburs. Those are summer weeds. Your first application needs to be about two weeks before the average date of your last killing freeze in your area. Learn that date and commit it to memory, because it’s one that will keep coming up for many gardening tasks. For those grassy weeds, apply Dimension, Halts or Balan.
Repeat the spring application 90 days later… These pre-emergents have a 100-day effective life, so you’ll need a booster shot three months after the first application. That will give you a full season of prevention against crabgrass and grassburs. We usually don’t have enough broadleafed weeds in the summer to justify the expense of Gallery granules.
Wonder why I didn’t mention use of “Weed-and-Feed” products even one time? I’m not a big advocate. Timing rarely works out that both need to be used at the same time. Plus there’s too much risk of harming trees and shrubs. Plus you rarely need to apply weedkillers over an entire lawn.